Automatic telephone system



AUTOMATIC TELEPHONE SYSTEM Filed May 26, 1933 WM fgg 30, 1936. H. v. ALEXANDERSSON 2,645,682

Patented June 30, 1936 PATENT OFFICE AUTOMATIC TELEPHONE SYSTEM.

Harald Valdemar Alexandersson,

Stockholm,

Sweden, assignor to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden Application May 26, 1933, Serial No. 673,057 In Germany June 6, 1932 3 Claims.

The present invention relates to such signalling and telephone systems in which a plurality of subscribers positions are connected to a common double line or party line and. in which calls are effected discriminately-through the actuation of selectors disposed at the subscribers positions.

In such systems it has proved to be of advantage to use one sourceof current for calls and dialled impulses and another source of current for setting of the selectors, it being hereby avoided to have the line when atrest, under a voltage of the order of magnitude required to render possible the operation of a plurality of distributed selectors. In known arrangements of this kind there has either been provided an extra circuit by means of earthing the apparatus, or two, different kinds of currents have been used, viz. alternating current and direct current. It is, however, particularly in railway telephony in connection with electrified railways, a disadvantage to use earthing, due to the danger of getting overvoltages to earth, and the use of alternating current along with direct current has involved such,

difficulties in connection with the setting of the selectors simultaneously with the occurrence of the dialled impulses that registers have had to be provided. The present invention renders possible the use of twosources of direct current without earthing the apparatus and without using registers.

According to the present invention this: is rendered possible thereby that the impulse sending and impulse receivingcircuits at the subscribers position areconnected as separate circuits, yet in parallel with each other and in series with current blocking devices, in such a manner to the double line that said impulse circuits together with the switching means of a controlling arrangement common to thedoubleline form direct current .circuits which are closed over said double line.

The present invention will now be described with reference-to the accompanyingdrawing, in which Figure 1 shows in principle a switching arrangement for a, party line and Figure 2 a detailed diagram for a subscribers set.

In the switching arrangement shown in Figure 1 GL is the common double line or partyline along which the different subscribers positions A1, A9 are distributed. For the setting up of talking connections there is provided a relay set R1 to R3 common to all subscribers" positions. In the subscribers? positions the drivingrnagnet SM of the selector and the dial F are connected in parallel to the party line GL. Further, the driving magnet SM and the dial-F are each connected in series with an appertaining rectifier L1 and L2 respectively, for example a cuprous oxide rectifier. In relation to the polarity of the line GL said rectifiers are turned in opposite directions.

The driving magnet SM is permanently connectedto the line GL through a rectifier L1 said rectifier being so, turned, however, that it doesnot pass; any current at the normal condition of voltage between the two branches of the lineGL. Neither can any current pass over the circuit extending through the dial F for the reason that saidcircuit is interrupted at a contact I of the switch hook KL. The selectors are assumed to be of the type the wipers of which are advanced one step for each current impulse.v A suitable type of selector is described in my copending. application No.

29,957. The said selector is a rotary selector which stops in the position at which it has come when the impulsing current ceases. Another type which may be used is a two-magnet selector in which both magnets are inserted. invthe im,-.

pulse-circuit. One of the magnets. is arranged, to actuate an armature fitted with a. ratchet, the

ratchet wheel being moved one step when the armature is attractedv The other magnet moves a ratchet which prevents the ratchet wheel moving backwards when the magnet is energized.

When both armatures are in rest position the. ratchet wheel is returned to home positionby a spiral spring similar to the escapement spring of a clockv When the ratchet wheel is in certain positions a contact is closed, as the armature of the stepping magnet lifts a contact spring towards the movable contact arms. The number of steps from the home position to the position of the ratchet wheel when this closing occurs corresponds to the calling number of the telephone to which the selector in question belongs. To the common line GL may, of course, be connected,

an arbitrary number of subscribers positions A.

In the arrangement shown on the drawing it has been assumed that nine subscribers positions are connected to the line GL, each subscribers position corresponding to one contact position on the selectors. If the line GL is connected to. a telephone exchange the selectors are also provided' with a contact position for calls to the telephone exchange in which position a selector is connected to the line GL.

The setting up of a talking connection between twov subscribers A1 and A9 connected to the line GL will now be described. When the subscriber A1 liftshis: microtelephone the switch hook KL closes acontactl, a circuit Zbeing then. formed through the dial F and two windings RL1 and RL2 of a relay R1 in the common relay set. The relay R1 operates and closes at its contact 3 a circuit for a relay R2 which in turn closes a circuit for a relay R3. When the latter relay operates it interrupts at its contact 4 the circuit through the relay R2, at the same time looking itself at its contact 5. During the short interval of time when the relay R2 is energized it causes interruption of the circuit 2 and connects via its contacts 6,1 in such a manner a current source to the line GL that the potential on the line is reversed. The driving magnets SM of all selectors connected to the line will then be actuated by a current impulse, the wipers of the selectors being then advanced one step from their home positions. The current source which by means of the relay R2 is connected to the line GL must as mentioned before have a voltage sufiicient for the operation of the selectors. Said source of current may of. course, if conditions permit, be the same source of current as is connected to the line GL through the relay R1. When the relay R2 is energized and the circuit 2 is closed the relay R1 will maintain its armature attracted on account of its winding RL1 being included in a circuit through a resistance r and the contact 6 of the relay R2. Through the advancing of the wipers of the selectors taking place in consequence of the call optical busying of the party line at the subscribers positions not involved in the connection may be obtained if the selector is arranged to operate a flatter or the like immediately upon leaving of the home or normal position. When the subscriber A1 dials the wanted number on his dial F a number of interruptions are effected in the circuit 2. For each such interruption the relay R1 opens its contact 3 for a moment, an interruption being then caused in the circuit of the relay R2 which immediately releases. When after a moment the relay R1 again closes the contact 3 a circuit is formed in the same manner as described above for therelay R3 which looks itself. and interrupts the circuit through the relay R2. During this period of time the relay R2 has caused the sending of a current impulse over the line GL, all driving magnets SM connected to the line having then been actuated. Consequently, each interruption in the circuit 2 causes the advancing of the wipers of the corresponding selectors one step. In case the subscriber A1 dialled number nine, here by causing nine current interruptions, the wipers will be advanced nine steps. Ringing signal is then effected at the connected subscribers station As, for instance, thereby that a special wiper of the selector K1 in Fig. 2 in the connecting position 8 in Fig. 2 of the selector closes a local galvanic circuit for a ringer B in Fig. 2. When the latter lifts his microtelephone the talking connection is completed. The current impulses sent over the line GL by the relay R2 have a duration which is exclusively dependent on the manner of operation of the relays R2 and R3 and independent of the impulse ratio of the dial. In this manner there is obtained with simple means an impulse correction which may be of advantage, particularly in trafiic between diiferent systems.

In the switching operation now described current impulses are sent by the relay R2 as soon as the relay R1 on account of the closing of the circuit 2 attracts its armature. It is, of course, also conceivable to arrange the circuits so that current impulses are sent over the line GL' by the relay R2 when the relay R1 releases on 3100 1111 O a interruption at the dial F in the circuit 2. This may be obtained, for example, by designing the contact 3 of the relay R1 as a resting contact. As in such a case the circuit extending through the dial F of the calling subscriber will be interrupted during the sending of the current impulses to the driving magnets SM, the rectifier L2 may be dispensed with.

At a call from the subscriber A1 to a subscriber which is not connected to the party line GL the subscriber A1 first dials a special number of in pulses, for example ten, whereby connection to the telephone exchange to which the line GL is connected is obtained, for instance, by means of a selector of the same type as those which are arranged at the subscribers positions. Thereupon the subscriber A1 dials the wanted number, the talking connection being then set up in the same manner as if the subscriber A1 had been an ordinary subscriber belonging to the telephone exchange in question.

When upon completion of the conversation the calling subscriber A1 rehooks his microtelephone the circuit 2 is interrupted at the contact- I and a relay R1 is deenergized as is also the relay R3. Upon completion of the conversation all selectors should be restored to their home positions. This can be efi ected in known manner either mechanically by means of spring power or by letting each selector operate as a self-acting step by step selector until it reaches its home position. Through a special arrangement of a rectifier in parallel with the driving magnet the selectors may, however, be restored in a simple manner by means of impulses sent over the line GL. The arrangement herefore will be more closely described in connection with the apparatus construction shown in Figure 2.

In the subscribers apparatus shown in Figure 2 the microphone M is fed from a local battery for the reason that battery supply from the exchange battery can become very varying on account of the diiferent line resistances occurring between the exchange and the subscribers sets on the same line. The telephone receiver T as well as the microphone M is inductively connected to the party line GL through an induction coil IR having three windings. In addition the apparatus contain an ordinary dial F, a switch hook KL, a trembler bell B, and a selector set consisting of a selector S with appertaining driving magnet SM and three rectifiers L1, L2, L3. The selector S has two difierent wipers K1, K2. One wiper K1 brings about the joining up of the bell B in a local circuit through the switch hook KL, and the other wiper K2 connects in its last position a rectifier L3 in parallel with the driving magnet SM which hereby becomes slow-acting. If the selectors along the line GL are restored in known maner by means of a train of impulses sent over the line GL the wipers of the selectors will first be advanced step by step to the last contact position in which the wipers remain until the train of impulses has ceased when they are moved to the first position. Consequently, said arrangement with a rectifier connected in parallel with the driving magnet in the first position renders possible the sending upon each clearing signal of a train of impulses containing a constant number of impulses. This number is so determined that all selectors are certainly restored to their home positions also if one impulse or another should not actuate a certain individual selector or i fa ome r a on the wipers of. the selectors should not occupy the same position at the beginning of the clearing. In the shown construction of the subscribers set the bell B is put into circuit by the Wiper K via a contact position 8 corresponding tothe number of the set and also via another contact position 9 common to all sets and being used at a simultaneous call to the sets along the line GL.

In the example shown on the drawing the driving magnets SM are connected in series with rectifiers L1 preventing current from passing through the driving magnets at the voltage condition normally existing between the two branches of the line GL. Provided that a higher voltage than the normal one is used for operating the selectors said selectors may be substituted by glow discharge tubes which are then so selected that they do not pass any current at the voltage used during calls and impulse sending from the dial. When the voltage thereafter is raised during the sending of current impulses to the driving magnets the glow discharge tubes will pass current and the driving magnets may be actuated. As in the latter case the voltage between the line branches is reversed no current will pass through the dials.

I claim:

1. In a telephone system a two wire party line, a number of telephone stations connected thereto, a controlling arrangement connected to the line and common to the said stations, an impulse sending and an impulse receiving circuit at each of the said stations connected to the double line in parallel with each other, step-by-step switches in the said impulse receiving circuits, and impulse senders in said impulse sending circuits, a rectifier inserted in each impulse receiving circuit, and a rectifier inserted in each impulse sending circuit, the said rectifiers being directed so that the said impulse circuits together with the said controlling arrangement form direct current circuits of opposite directions over the common two wire party line and switching means in the common controlling arrangement allowing a continuous stepping of the different step-by-step switches from an impulse sending circuit during the impulse sending.

2. In a telephone system a two wire party line, a number of telephone stations connected thereto, a controlling arrangement connected to the line and common to the said stations, an impulse sending and an impulse receiving circuit at each of the said stations connected to the double line in parallel with each other, step-by-step switches in the said impulse receiving circuits, and impulse senders in said impulse sending circuits, a rectifier inserted in each impulse receiving circuit and a rectifier inserted in each impulse sending circuit, the said rectifiers being directed so that the said impulse circuits together with the said controlling arrangement form direct current circuits of opposite directions over the common two wire party line, switching means in the common controlling arrangement allowing a continuous stepping of the different step-by-ste'p switches from an impulse sending circuit during the impulse sending and a further rectifier which is connected to the last contact position of the stepby-step switch so as to form a shunt to the same.

3. In a telephone system a two wire party line, a number of telephone stations connected thereto, a controlling arrangement connected to the line and common to the said stations, an impulse sending and an impulse receiving circuit at each of the said stations connected to the double line in parallel with each other, step-by-step switches in the said impulse receiving circuits, and impulse senders in said impulse sending circuits, a rectifier inserted in each impulse receiving circuit and a rectifier inserted in each impulse sending circuit, the said rectifiers being directed so that the said impulse circuits together with the said controlling arrangement form direct current circuits of opposite directions over the common two wire party line, switching means in the common controlling arrangement allowing a continuous stepping of the different step-by-step switches from an impulse sending circuit during the impulse sending and a relay set at the controlling arrangement which sends impulses to the step-by-step switches which are independent of the impulse ratio of the dial.

HARALD VALDEMAR ALEXANDERSSON. 

